1. Field of the Invention
The present invention generally relates to television receivers or tuners, and more specifically to tuner front-end signal processing.
2. Related Art
Currently, amplifiers are used in television receiver front-end circuits. However, these front-end circuits do not include any frequency selectivity. Instead, they take the entire television frequency band. This works well for cable television for which the power of all the channels is relatively even and well-controlled. However, for a terrestrial television receiver, there can be very large power differences from one channel to another channel.
In addition, existing discrete (“canned”) tuners include filters that are implemented with high-quality discrete components and varactor diodes to perform the tuning. However, this does not fit with a preferred paradigm of an integrated circuit with a few non-critical external components.
Also, television receivers require very large dynamic range and have potentially strong interfering signals in the same frequency band. The large dynamic range is necessary to receive signals over a large range of input power. It is also important for television receivers to maintain a good input match to the cable or antenna impedance (typically about 75 ohms) and to change gain smoothly in response to signal level variations. A smooth change in gain avoids picture disturbances and error bursts. These requirements constrain the approaches that can be used to improve dynamic range.
Increasingly, consumer products are requiring multiple tuners connected to a single source. This permits functions such as watch-and-record (such as Digital Video Recording (DVR)), picture-in-picture, and simultaneous data/video reception, among many other functions currently available and being developed. This further constrains the receiver design. For example, filtering to eliminate unwanted distortion must be implemented in a way that does not affect reception of the interfering channel by another tuner.
What is needed is a television tuner front-end that provides high dynamic range, selectivity, and the ability to drive multiple tuners without degradation.